FWIW, I leave batteries in RF-602, RF-622 and 560-TX transceivers all the time and never had a problem in any of the 15 or so units I have. I only take the batteries out of my flashes because I have a bunch and only consistently use 2 or 3 of them.
If you leave batteries in the RF-602 trigger you are bound to have a flat batery when you come to use it if left in a camera bag, it doesn't have an On/Off button!
I cut a toilet paper roll tube in half, put duct tape on one side, and stuffed the other side with some tissue. The trigger fits in nice and comfy and doesn't touch the test button. I keep an extra CR2 battery in my bag just in case, but I've been using the tube case for about 3 years now and never had an issue.